An LED device is a semiconductor device that includes an interface, or junction, between two types of semiconductor material, one being a p-type semiconductor and the other being an n-type semiconductor. The LED is a special type of diode that emits light. When biased in one direction, a current flows through the device, but when biased in an opposite direction, current does not flow unless in a reverse saturation current mode.
With an appropriate voltage applied across two leads of the device, a light (radiation) is produced which includes a color corresponding to the type of material used to make the semiconducting material of the LED. The LED device has applications in many industries and many types of devices. Since the LED is widely used, the cost of LED devices is generally very low and cost effective. Consequently, the LED device can be found in many different types of electrical products and devices due its ability perform as a low-cost switch or low-cost source of light. Furthermore, it is known in the art, though less well appreciated, that LEDs can absorb radiation to produce an electrical signal though they are seldom used for this application.
It is known in the art that LEDs are relatively selective in both an emission spectrum of light at a particular wavelength, and an absorption spectrum or reception of light of a particular wavelength. LEDs typically absorb radiation with a spectrum that is higher energy and smaller wavelength than the spectrum at which the light is emitted.
Because LEDs also detect light, there are various mechanisms for determining the content of optical signals incident upon an LED junction. For instance, it is possible to measure the light levels incident upon an LED while it is emitting light by measuring the difference it creates in junction impedance. For an LED junction which is not emitting light, it is possible to measure a current which flows with the diode in an under reversed biased condition. For instance it is possible to measure this current directly (e.g. with a picoammeter). Another mechanism for measuring incident light flux is to directly measure the photovoltage generated by illumination. Another mechanism for measuring incident light flux integrated over time is to apply a known reverse bias across the junction (as a capacitive stored charge) and then measure the decay of this voltage value over time. This last mechanism provides a mechanism for simplifying the electronics needed and reducing noise by providing an intrinsically time-integrated data output.
LED behavior can also depend upon the junction temperature of the device. In some embodiments, temperature can be monitored to enable dynamic referencing and calibration for the device. As is known in the art, the temperature measurement and/or control of an LED may be accomplished in a variety of ways.
Even though LED operating characteristics and behaviors are known, LEDs are inefficient absorbers and therefore are generally not used as such for the determination of the characteristics of a physical environment including chemical and physical environments. Consequently, there is a significant need for the unique LED devices, methods, systems and techniques disclosed herein. In addition, there is a significant need for the unique apparatuses, methods, systems and techniques disclosed herein.